/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.hadoop.tools;

import java.io.IOException;
import java.io.PrintStream;
import java.net.InetSocketAddress;
import java.util.List;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.hdfs.DFSUtil;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;

/**
 * Tool for getting configuration information from a configuration file.
 * 
 * Adding more options:
 * <ul>
 * <li>
 * If adding a simple option to get a value corresponding to a key in the 
 * configuration, use regular {@link GetConf.CommandHandler}. 
 * See {@link GetConf.Command#EXCLUDE_FILE} example.
 * </li>
 * <li>
 * If adding an option that is does not return a value for a key, add
 * a subclass of {@link GetConf.CommandHandler} and set it up in 
 * {@link GetConf.Command}.
 * 
 * See {@link GetConf.Command#NAMENODE} for example.
 * </ul>
 */
public class GetConf extends Configured implements Tool {
  private static final String DESCRIPTION = "hdfs getconf is utility for "
      + "getting configuration information from the config file.\n";

  enum Command {
    NAMENODE("-namenodes", new NameNodesCommandHandler(),
        "gets list of namenodes in the cluster."),
    INCLUDE_FILE("-includeFile", new CommandHandler("dfs.hosts"),
        "gets the include file path that defines the datanodes " +
        "that can join the cluster."),
    EXCLUDE_FILE("-excludeFile", new CommandHandler("dfs.hosts.exclude"),
        "gets the exclude file path that defines the datanodes " +
        "that need to decommissioned.");

    private final String cmd;
    private final CommandHandler handler;
    private final String description;

    Command(String cmd, CommandHandler handler, String description) {
      this.cmd = cmd;
      this.handler = handler;
      this.description = description;
    }

    public String getName() {
      return cmd;
    }
    
    public String getDescription() {
      return description;
    }
    
    public static CommandHandler getHandler(String name) {
      for (Command cmd : values()) {
        if (cmd.getName().equalsIgnoreCase(name)) {
          return cmd.handler;
        }
      }
      return null;
    }
  }
  
  static final String USAGE;
  static {
    Configuration.addDefaultResource("hdfs-default.xml");
    Configuration.addDefaultResource("hdfs-site.xml");
    
    /* Initialize USAGE based on Command values */
    StringBuilder usage = new StringBuilder(DESCRIPTION);
    usage.append("\nhadoop getconf \n");
    for (Command cmd : Command.values()) {
      usage.append("\t[" + cmd.getName() + "]\t\t\t" + cmd.getDescription()
          + "\n");
    }
    USAGE = usage.toString();
  }
  
  /** 
   * Handler to return value for key corresponding to the {@link Command}
   */
  static class CommandHandler {
    final String key; // Configuration key to lookup
    
    CommandHandler() {
      this(null);
    }
    
    CommandHandler(String key) {
      this.key = key;
    }

    final int doWork(GetConf tool) {
      try {
        return doWorkInternal(tool);
      } catch (Exception e) {
        tool.printError(e.getMessage());
      }
      return -1;
    }
    
    /** Method to be overridden by sub classes for specific behavior */
    int doWorkInternal(GetConf tool) throws Exception {
      String value = tool.getConf().get(key);
      if (value != null) {
        tool.printOut(value);
        return 0;
      }
      tool.printError("Configuration " + key + " is missing.");
      return -1;
    }
  }
  
  /**
   * Handler for {@link Command#NAMENODE}
   */
  static class NameNodesCommandHandler extends CommandHandler {
    @Override
    int doWorkInternal(GetConf tool) throws IOException {
      tool.printList(DFSUtil.getNNServiceRpcAddresses(tool.getConf()));
      return 0;
    }
  }
  
  private final PrintStream out; // Stream for printing command output
  private final PrintStream err; // Stream for printing error

  GetConf(Configuration conf) {
    this(conf, System.out, System.err);
  }

  GetConf(Configuration conf, PrintStream out, PrintStream err) {
    super(conf);
    this.out = out;
    this.err = err;
  }

  void printError(String message) {
    err.println(message);
  }

  void printOut(String message) {
    out.println(message);
  }

  void printList(List<InetSocketAddress> list) {
    StringBuilder buffer = new StringBuilder();
    for (InetSocketAddress address : list) {
      buffer.append(address.getAddress().getHostAddress()).append(" ");
    }
    printOut(buffer.toString());
  }

  private void printUsage() {
    printError(USAGE);
  }

  /**
   * Main method that runs the tool for given arguments.
   * @param args arguments
   * @return return status of the command
   */
  private int doWork(String[] args) {
    if (args.length == 1) {
      CommandHandler handler = Command.getHandler(args[0]);
      if (handler != null) {
        return handler.doWork(this);
      }
    }
    printUsage();
    return -1;
  }

  @Override
  public int run(final String[] args) throws Exception {
    return doWork(args);
  }

  public static void main(String[] args) throws Exception {
    int res = ToolRunner.run(new GetConf(new Configuration()), args);
    System.exit(res);
  }
}
